Black flies are among the most medically-important insects in the world, due principally to their role in the tropics as vectors of the filarial nematode causing human river blindness (onchocerciasis). Ever since the discovery of the pathogenicity of Bti (Bacillus thuringiensis var. israelensis) to black flies, there has been an interest both in tropical and temperate climates to use this bacterium in operational black fly control programs. Short-term field trials have attempted to identify nontarget stream insects which might be killed by Bti, but long-term comprehensive studies of the affect of repeated applications of Bti on stream insect communities have been lacking. The currently-funded research project (AI-15605) years 04-06) was specifically designed to address this need. Now in its third year, two years of data have been generated on the naturally-occurring insect population levels in upstream and downstream areas of the study steam, Camden Creek. At the present, Camden Creek is being repeatedly treated with Bti to eliminate all black flies from its downstream section (the upstream sampling site is continuing to serve as the "control"). Data on the abundance of insect populations during the current treatment year, when compared with the data generated from samples taken during the preceding two untreated years, will provide a means with which to assess the environmental impact of Bti on the stream insect community. The present proposal requests a two-year extension of this Camden Creek study. This would allow one additional year of treatment and sampling, followed by a year in which the processing and analysis of all benthic samples would be completed. With this additional year of sampling, the two years of pretreatment data already obtained on the population levels of Camden Creek's benthic insect taxa could be directly compared with data generated during two treatment years. The data obtained from this additional treatment year would be critically important for confirming trends in insect population levels, and thus would provide increased confidence in the assessment of the environmental impact of Bti.